Work around Ruby 2.5.3 crash when a CI job is selected

Ruby 2.5.3 in combination with Rails 5 appears to crash in development
when a CI job is selected for a runner. For some reason, the return
inside the block seems to seg fault. Let's get rid of this since
this isn't a good coding practice in any case.

Relates to https://gitlab.com/gitlab-org/gitlab-ce/issues/54281

Also see https://bugs.ruby-lang.org/issues/15325.

app/services/ci/register_job_service.rb

@@ -36,7 +36,7 @@ module Ci
         builds = builds.with_any_tags
       end
 
-      builds.find do |build|
+      selection = builds.find do |build|
         next unless runner.can_pick?(build)
 
         begin
@@ -45,7 +45,7 @@ module Ci
           if assign_runner!(build, params)
             register_success(build)
 
-            return Result.new(build, true) # rubocop:disable Cop/AvoidReturnFromBlocks
+            break build
           end
         rescue StateMachines::InvalidTransition, ActiveRecord::StaleObjectError
           # We are looping to find another build that is not conflicting
@@ -61,6 +61,8 @@ module Ci
         end
       end
 
+      return Result.new(selection, true) if selection
+
       register_failure
       Result.new(nil, valid)
     end